The present invention generally relates to a universal parallel ruler for a three-dimensional drawing such as an isometric, dimetric or anisometric projection. Basically, the three-dimensional drawing is defined by three planes and all the circles contained to these three planes, corresponding to holes, shafts, etc., are drawn as ellipses. Each ellipse is determined by the ratio of its major and minor axes. The practical operation of drawing is performed using a template including many ellipses of various ratios arranged therein. In the universal parallel ruler for three-dimensional drawing of the prior art, in which three scales correspond to the basic three axes, one of the serious problems with the prior art ruler lies with the fact that three scales interfere with one another for effective use of the template. Each of the ellipses drawn in the basic three planes is determined by major and minor axes which are always perpendicular to each other. In view of these aspects, it would be extremely advantageous to have a universal parallel ruler, two scales which are always held perpendicular to each other for three-dimensional drawing because the template can be used without any interference with the respective scales and, further, the respective basic three axes and lines transverse to each of these basic three axes would be immediately obtained.
Although the means to set the scales at an interval of 15 or 30 degrees by cooperation of an index plate mounted on a head support and a locking pawl provided on the movable part of the head (i.e., on the scale side) is well known in the field of universal parallel rulers having two scales perpendicular to each other, it has been difficult to set the scales at intermediate angles which correspond neither to 15 degrees nor to 30 degrees. The same problem remains even when the index plate is movably arranged and adapted to the fixed at an optional position relative to the associated support, since only one of the basic three axes could be position-set and rest of the two axes have positions which are for every three-dimensional drawing.
In accordance with the present invention, the problem as described just above is overcome by an arrangement such that the head is provided with preset stoppers principally adapted to be optionally position-adjusted according to the basic three axes of a three-dimensional drawing and the scales can be selectively set to the basic three axes and can vary for every three-dimensional drawing. The preset stopper corresponding to the vertical axis of the basic three axes of the three-dimensional drawing may be stationarily provided since said vertical axis is in most cases drawn as a vertical line.
Also, according to the present invention, there is provided an arrangement such that a single locking piece is engaged with or disengaged from the preset stoppers respectively corresponding to the basic three axes so that the scales may be selectively set to to the respective preset stoppers which have been angularly set.
In a further preferred embodiment, the angularly preset stoppers can be fixably mounted by associated clamp members on the protractor and thereby the basic three axes can be independently set.
The present invention also provides a universal parallel ruler for three-dimensional drawing in which the scales can be set by operatively associating the protractor with the scales relative to a stationary index and fixing the protractor at a desired position to represent the three axes.
Accordingly, one object of the present invention is to provide a universal parallel ruler having scales which are fixedly mounted in perpindicular relationship with each other, yet maintain flexibility necessary for adjusting the scales for a variety of three-dimensional axes.
Another object of the present invention is to provide three preset stoppers which are engagable with the scales thereby permitting the scales to be angularly and adjustably varied in position relative to the preset stoppers coming into locking engagement with the preset stoppers. Another object of the present invention is to permit the preset stoppers to be angularly adjustable. Still another object of the present invention is to permit the preset stoppers to be fixedly or removably mounted onto the protractor portion of the parallel ruler so that the three axes of the three-dimensional drawing may be independendantly set.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.